Burner control system



Oct. 19, 1943. SHAW 2,332,269

BURNER CONTROL SYSTEM Filed April 1-4, 1941 Patented Oct. 19, 1943 BURNER CONTROL SYSTEM Burton E. Shaw, Bristol, 1116., assignor to Penn 1 Electric Switch (30., Goshcn, Ind., a corporation of Iowa Application April 14, 1941, Serial No. 388,564

Claims.

My present invention relates to a burner control system including a'low'voltage protection feature and a combustion temperature switch of the type disclosed in the Rothwell and Wagne application, Serial No. 378,150, filed February 10,

1941, which eliminates the necessity of the usual slip or friction connection used in presentday stack switches.

' One object of my invention isto provide a protection system of simple and inexpensive construction for bumer control circuits.

A further object is to provide in connection. with a bumer' control circuit, a protection feature particularly for low voltage wherein a single relay or the like is. operable-to cut in at as low as eighty percent of the full line voltage and to cut out at a point not lower than approximately sixty-five percent of the full line voltage, whereas in the usualsystems in which relays are used .for' burner control circuits, the relay when properl'y designed to give sufflcient motion for operation of the contacts cuts out-at about thirty-five percent of the full line voltage. This is particularly important because at about sixty percent of the full line voltage the burner functions improperly, itsefnci'ency is low, the air velocity and oil pressure being decreased and the opening of the solenoid or pressure regulating valve which usually controls the oil supply is restricted. Also, low voltage in :the ignition transformer occurs. which causes entire loss of or at least irregular spark. This results in the burner popping, and sometimesin'an explosion.

The problem is particularly present in small localities when current consumption varies greatly, andin most of the localities whensleet gathers on the transmission wires and causes a temporary dropin voltage which may last for sometimes an hour or more. It is therefore obvious that cut out of the relay at or above sixty-five percent of the full line voltage is desirable.

A further object of my invention is to provide a relay which can be'cut in at one voltage and thereafter maintained in the cut-in position by a reduced voltage, so that it is easier to drop out upon subsequent line voltage drop and the dropping out of the relay will occur before an excessive drop in the full line voltage occurs, whereas if the initial current supply, instead of a reduced current supplydue to, such reduced voltage, were maintained for keeping the relay energized, the

' line voltage at which the relay drops out would be excessively low.

Still .a further object is to provide a, combustion switch in the control system which is extremely simple in construction and inexpensive to manufacture and which may be arranged to respond to combustion by exposing a certain bimetal of the combustion switch to heat radiated from the combustion chamber, it being unnecessary to locate the thermostat inside a stack or the like, or inside the combustion chamber, but merely externally of the chamber with an opening through the wall of the chamber to expose the bimetal element to the heat therein.

With these and other objects in view, my invention with respect to its features which I believe to be novel and patentable will be pointed out in the claims appended hereto. For a better detailed understanding of the invention, and further objects relating to details of economy of my invention, reference is made to the following description and to the accompanying drawing wherein such further objects will definitely appear, and in which Figure l is an electrodiagrammatic view of a burner control system embodying my invention, the combustion switch being shown in cold position;

Figures 2, 3 and 4 show, respectively, the combustion switch in the hot, initial combustion failure, and combustion failure after established, positions;

Figure 5 is a diagrammatic view of a portion of Figure 1 showing a slight modification, with the burner in non-operating position, and

Figures 6 and 7 are views of a holding switch of Figure 5 in an intermediate and in a running position, respectively.

On the accompanying drawing, I have used the reference character BM to indicate a burner motor and B a burner operated thereby. Ign indicates ignition mechanism for the burner B. A motor switch MS controls energization of the burner motor and the ignition mechanism, with current being supplied through wires I9 and 20. The wires I9 and 20 also extend to the primary P of a transformer T.

A room thermostat RT is illustrated and a control circuit therefor is energized initially from the entire secondary S of the transformer T. The initial secondary circuit includes combustion switch contacts I4 and I5, a relay coil RC and a safety heater H. The combustion switch for the contacts. I 4 and I5 is indicated generally at CS and includes a pair of bimetal elements In and I2 anchored as to a support I3 of insulating material. The contacts I4 and I5 are carried by the bimetal element l0 and I2, respectively.

The bimetal element I0 carries a support It for a permanent magnet I1 which is adapted to cooperate, for a purpose which will hereinafter appear, with an armature I8. The armature I8 is carried by the bimetal element I2. The combustion switch CS is preferably mounted just outside a combustion chamber CC with an opening I I in the wall of the chamber to permit radiation of combustion heat to the element III.

The transformer T has its secondary coil S provided with a center tap indicated at 24. A holding switch HS is connected with the tap I4 and with the room thermostat or control circuit at a point intermediate the heater H and the relay coil RC. The holding switch HS is adapted to be closed by the relay coil RC whenever it is energized and the motor switch MS is adapted to be likewise closed.

In'Figures 5, 6 and 7, I show a modified ar-' rangement wherein a holding switch HS takes the place of the holding switch HS and includes a pair of stationary contact blades 2| and 22, and a movable blade 23. The movable blade 23 normally assumes the position shown in Figure 5 but upon energization of the relay coil RC is moved thereby to the position of Figure 7. In passing from the position of Figure 5 to the position of Figure 7, the intermediate position of Figure 6 is assumed wherein the contacts of the holding switch HS overlap.

PRACTICAL OPERATION FIGURES 1 TO 4 Normal burner operation With the combustion switch in the cold position of Figure 1, closure of the room thermostat effects energization of the relay coil RC and the heater H through the combustion switch contacts I4 and I5 fromthe entire secondary S of the transformer T. Energization of the relay coil effects closure of the motor switch MS, whereby the burner motor BM and the ignition mechanism Ign of the burner are energized.

Energization of the relay coil RC also closes the holding switch HS so that instead of the initial room thermostat or control circuit, two circuits are established as follows:

(1) The lower half of the secondary S supplies current to the heater H;

(2) The upper half of the secondary S supplies current to the relay coil RC through the room thermostat and the combustion switch contacts I4 and I5.

Assuming the secondary voltage to be 25, there are twenty-five volts available for causing cut-in f of the relay when the thermostat closes. The parts are so designed that the relay can cut-in at eighty-five percent of this value so that the relay is thus operable at anywhere above eighty per cent of the full line voltage supplied to the primary P. r

'As soon as the holding switch HS is'closed by energization of the relay, the circuits 1 and 2 mentioned above are established and obviously are weaker than the initial current from the entire secondary S. Consequently, the gaps in the relay can be quite wide and yet the relay will cut-out upon only a substantially small drop in the normal line voltage.

Energization of the heater H causes the bimetal element I2 to be heated and thereby warped, but this is a relatively slow process. Accordingly, the bimetal element I2 does not warp enough to separate the contact I5 from the contact I4 before combustion chamber temperatures start warping the bimetal element III so that the contact I4 follows up the contact I5, as in Figure 2. The magnet I1 and the armature I8 also aid in keeping the contacts I4 and I5 engaged. The bimetal elements I0 and I2 may be placed under some initial tension when mounted on the insulating block I3, if it is desirable to eliminate the armature and magnet.

Subsequently, when the room thermostat opens, the relay coil is de-energized to thereby open the motor switch and stop the burner. The parts II] and I2 will then cool down to their initial positions as in Figure 1 for another burner operating cycle.

Failure of combustion to be established Referring to Figure 3, if combustion does not occur in the normal manner, the bimetal element I0 will remain in its cold position while the bimetal element I2 will move to its hot position, due to energization of the heater H. This will take preferably about a minute or so, although the time does not have to be as long as it takes the usual safety switch in a stack switch installa- Combustion failure after combustion has been established Referring to Figure 4, combustion has been established, thus moving the parts of the combustion switch to the position of Figure 2, and then combustion has failed so that the bimetal element Ill begins to bend back toward its original position, due to cooling down of the combustion chamber. Accordingly, the contact I4 will leave the contact I5 when the energy built up by straightening of the bimetal element issufficient to overcome the pull of the magnet I! on the armature I8. The contacts I4 and I5 thereupon open with snap action. The relay coil is now de-energizedso that the motor switch opens and a purging period will be provided. during which the elements I0 and I2 cool to their initial positions. The contacts I4 and I5 are thereupon re-engaged to recycle the burner.

The combustion switch CS is a combined combustion switch and safety switch in that the contacts I4 and I5 are separated as a result-of a cold combustion chamber CC and a hot heater H. Whenever these two events occur at the same time, then the burner is shut down for a purging period and recycling. As long as the burner operateson normal cycles, the contacts I4 and I5 remain engaged and are never separated. Separation occurs only when there is either an initial combustion failure or a combustion failure subsequent to combustion establishment.

Frames 5, 6 AND 7 The system shown in these figures operates in substantially the same manner as described in connection with Figures 1 to 4 with the difference that energization of the relay'coil effects reduction of the current supplied thereto for protection purposes by the double-throw holding switch HS. The initial room thermostat circuit is from the bottom of the secondary S through the relay: coill' the heater; the'combustion switch and the, room thermostat 'tothe top. of thecoili S. Energization of mammacoil positions the holdingi switch: H51 asdn- Figure 'h sothat, instead of theainitial circuit; thereis -then-acircuit through the relay coil, the heater, the-combustion switch and the room th'ermostaty with the elements 22 and in. suchcircuit and theupper half of the secondary S entirelw out" of the circuit. The overlapping: of: the contacts, as in Figure 6, I preventsany opening of therelay coil circuit which would 'pennit it to revertto initialposition during change-oven some ch'anges may be made in the construction and'arrange'menti ofi'the parts of my device Without departing-from the real 'spirit and purpose of" my invention, I and it is my intention to coverby my' claims 'any modifled formsof I structuretor-use of mechanioal equivalents which may bereasonably included I within -their scope with-- out sacrificing any of theadvantages thereof; lI 'claim as my inventions i 1 A burner control systemcomprising a burnerr-a motor for operating said: burner, an 'operating circuit for said burrier including a motor switch, a'-- source orwcmene for said circuit, a transformer cohneoted with said source and having a tapped secondary, a room thermostat, a circuit therefor, combustion switch contacts and a safety heater in said circuit, a combustion switch including said combustion switch contacts and a pair of exposed bimetal elements, one responsive to heat of the combustion chamber and located entirely outside of it, the combustion chamber having an opening through which heat is radiated to said one bimetal element, the other bimetal element being responsive to heat of said safety heater, said combustion switch contacts being carried by said bimetal elements to be normally engaged with each other when the bimetal elements are cold, while they are heating and cooling and while they are hot, armature and magnet means for producing snap action of, and tending to close said contacts, said bimetal elements upon the one heated by the safety heater remaining heated and the other one cooling, opening said contacts, and upon said other one remaining cold and the one heated by the safety heater being heated, opening said contacts a predetermined time period after the safety heater is energized, said room thermostat circuit including a relay coil serially connected with said safety heater and initially with the end ter minals of said secondary, said relay being constructed to close said burner switch when energized in response to closure of said room thermostat, and means operated by said relay upon energization thereof to connect the tap of said secondary to said room thermostat circuit between said safety heater and said combustion switch to thereby reduce the holding current in said relay coil and enable the same to open upon a predetermined minimum fall of line voltage.

2. In a burner system, a transformer, an initial room thermostat circuit including a room thermostat, means operable upon energization by the secondary of said transformer to initiate operation of the burner, a safety heater and combustion switch contacts, a pair of temperature responsive elements carrying said combustion switch contacts, one of said elements being responsive to the heat of said safety heater and the other being located exterior of and responsive to heat radiated from a combustionchamber, said combustion switch contacts being normally encased when the temperature responsive ele ments are eith'encold or. hot. and I disengaged only when the safety. heater heated one is hot and the-combustionchamber heated one is cold, said safety heater and said contacts.- being included insaid initial'room thermostats circuit whereby (10- upon closure ofv the room thermostat, operationof the-burner is initiated; (2) uponheating of: both of said temperature responsive elements the burner circuit is maintained energized; (3) upon separation: of: said combustion switch contacts as a result of combustion failure after it has occurred the room. thermostat circuit is opened at the'combustioni switch, and (4) upon heating of the temperature responsive element heated by the safety heater andthe temperature responsive element heated by thecombustion chamber remaining in its cold position said combustion switch contacts are openedr after a time period determined by theeffe'ct of the safety heater on the temperature responsive element heated thereby, a second circuit energized by aportion only of said secondary of said transformer and including said room thermostat, saidrelay coil and said combustion switch-contacts, holding contacts forestablishing said second circuit and for maintaining it as long as said combustion switch contacts "are engaged with each other, said holding contacts being closed by energization of said means, and a third circuit energized by the remaining portion of said secondary and including said safety heater only, said second and third circuits being established and said initial room thermostat circuit being altered as to current supplied thereto by closure of said holding contacts.

3. In a burner protection system, a transformer, an initial room thermostat circuit including a room thermostat, means operable upon energization by the secondary of said transformer to initiate operation of the burner, combustion switch contacts, a pair of temperature responsive elements therefor, a heater for one of said temperature responsive elements, the other one being responsive to the temperature of a combustion chamber and being located between the combustion chamber and said one of said temperature responsive elements, and a control circuit interconnecting the foregoing elements and operating upon closure of said room thermostat to (1) energizesaid means and thereby operate the burner and to energize said heater, and (2) to open said room thermostat circuit at said combustion switch contacts when they are separated by combustion failing to occur or failing after occurrence, a second circuit energized by a portion only of said secondary of said transformer and including said room thermostat, said combustion switch contacts and said means, holding contacts for establishing said second circuit and for maintaining it as long as said combustion switch contacts are engaged, said holding contacts being closed by energization of said means, and a third circuit energized by the remaining portion of said secondary and including said heater only, said second and third circuits being established and said initial room thermostat circuit being altered as to the current supplied thereto by operation of said means as a result of room thermostat closure effecting closure of said holding contacts.

4. In a control system for burners including a protection feature, a transformer having an intermediate tap for furnishing two sources of current supply, an initial room thermostat circuit connected across said transformer and including a room thermostat to initiate operation ofrthe burner, a heating element and a combustion switch in said initial room thermostat circuit, said combustion switch comprising a pair of bimetal elements and a pair of contacts, one of said contacts being carried by each element, one of said elements being responsive-to combustion chamber temperatures and located outside of the combustion chamber, and the other being responsive to heat from said heating element and located between said heating element and said first element with the first element between said second element and the combustion chamber, an armature carried by one of said bimetal elements, a magnet cooperating therewith and carried by the other bimetal element to keep said contacts in engagement and effect snap action thereof toward open position when the energy in said bimetal elements is such as to overcome the pull of the magnet on the armature, holding contacts closed by energization of said means and connected with said initial room thermostat circuit for dividing it so that upon closure of the holding contacts a second circuit is established through said room thermostat, said means and said combustion switch contacts, and a third circuit is established through said heating ele-' ment, said combustion switch contacts, upon opening, discontinuing said third circuit.

5. A control system of the character described comprising a transformer, a room thermostat circuit including combustion switch contacts and a heater, a combustion switch including said contacts and a pair of temperature responsive elements, one of which responds to said heater and the other located exterior of and responding to temperature radiated directly from a combustion chamber, a relay operable upon energization to cause operation of the burner, a circuit including the secondary of said transformer and said relay and controlled by a room thermostat which establishes said circuit upon closure of the thermostat, and means thereafter operable to maintain said relay energized from one portion only of said secondary and said heater energized from the remaining portion thereof, said temperature responsive elements being efl'ective to normally retain said combustion switch contacts engaged when both temperature responsive elements are cold or hot, and to open them when the one heated by the heater is hot and the one heated by the combustion chamber is cold.

BURTON E. SHAW. 

